Appendix A, which is a part of the present disclosure, is a microfiche appendix consisting of 5 sheets of microfiche having 400 frames. Microfiche appendix A includes a software program operable in a microprocessor controller of a left/right line locator as described below.
A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever.
This and other embodiments are further described below.
1. Field of the Invention
The invention relates to a line locator for locating concealed conductors and, more specifically, to line locators having the capability of determining the lateral location of the line locator relative to the concealed conductor.
2. Background
It is often necessary to locate buried conduits, which are employed by numerous utility companies, in order to repair or replace them. In addition, it is important to locate conduit lines in order not to disturb them when excavating for other purposes (such as, for example, addition of new conduits). Examples of buried conduits include pipelines for water, gas or sewage and cables for telephone, power or television. Many of the conduits are conductors, such as metallic pipelines or cables. In other applications, it is often useful to locate concealed elongated conductors, such as power lines or copper water lines, concealed in the walls of buildings. It is well known to locate concealed elongated conductors (xe2x80x9clinesxe2x80x9d) by detecting electromagnetic emissions from them.
A conducting conduit (a line) may be induced to radiate electromagnetically by being directly connected to an external transmitter or by being inductively coupled to an external transmitter. In some instances, such as with power lines, the line may radiate without an external transmitter.
A line locator detects the electromagnetic radiation emanating from the line. Early line locators included a single sensor that detects a maximum signal or a minimum signal, depending on the orientation of the sensor, when the line locator is passed over the line. Later line locators have included two sensors to provide information regarding proximity to the line.
FIG. 1 shows a line 4, beneath surface 7, that is radiating a magnetic field 5. Magnetic field 5 is generally directed in a circular fashion around line 4. Line locator 1 is held by operator 6 over line 4. Line locator 1 includes sensor 3 that detects magnetic field 5 and displays a signal on a display 2 that is indicative of the magnetic field strength at sensor 3. Depending on the orientation of sensor 3 (i.e., whether it is sensitive to horizontal or vertical components of the magnetic field), display 2 will indicate a maximum signal or a minimum signal when line locator 1 is held directly above line 4 (where the magnetic field 5 is directed horizontally).
For purposes of this description, a horizontal magnetic field refers to a magnetic field directed parallel with surface 7, even if surface 7 happens to be a wall. A vertical magnetic field refers to a magnetic field that is directed perpendicular to surface 7. Similarly, a horizontally oriented sensor is arranged to detect horizontal components of the magnetic field while a vertically oriented sensor is arranged to detect vertical components of the magnetic field.
FIG. 2A shows a line locator 200 having a left sensor 201, a right sensor 202, and a center sensor 203, each of the sensors being vertically oriented. Left sensor 201 and right sensor 202 are positioned at equal elevation above surface 7 and have substantially identical responses to magnetic fields. Center sensor 203 is disposed equidistant from left sensor 201 and right sensor 202 and can have an elevation above surface 7 that is different from the elevation of left sensor 201 and right sensor 202. Center sensor 203 is a compensating field sensor that is used to correct for ambient magnetic fields (i.e., magnetic fields that do not originate from line 4) in the vicinity of left sensor 201 and right sensor 202. As indicated by the dots drawn adjacent each sensor, center sensor 203 is arranged such that, given the same magnetic field, the output signals from center sensor 203 will have the opposite polarity of the output signals from left sensor 201 and right sensor 202.
In general, a transmitter 205 is electrically coupled to line 4 so that line 4 will radiate with a frequency determined by transmitter 205. Line locator 200 is capable of detecting whether line 4 is to the left or the right of center sensor 203 by comparing the magnetic field 5 at left sensor 201 with the magnetic field 5 at right sensor 202. U.S. Pat. No. 4,639,674, entitled xe2x80x9cApparatus and Method Employing Extraneous Field Compensation for Locating Current-Carrying Objects,xe2x80x9d issued Jan. 27, 1987, to Rippingale, describes such a line locator.
FIG. 2B shows detection circuitry for line locator 200 of FIG. 2A. The output signal from center sensor 203 is added to each of the output signals from left sensor 201 and right sensor 202 such that a correction is made for ambient magnetic fields not associated with line 4 (see FIG. 2A). The corrected output signal from left sensor 201 is processed through a channel comprising, in series, a pre-amplifier 204, a mixer 205, an IF filter/amplifier 207, and a phase detector 210. The corrected output signal from right sensor 202 is processed through a substantially identical channel.
In each channel, mixer 205 combines the output signals from pre-amplifier 204 with a LO FREQ signal from local oscillator 206. The LO FREQ signal is the frequency of transmitter 205 (see FIG. 2A) plus a center frequency. IF Filter 207 is a band pass filter and amplifier that passes signals at the center frequency. The combination of mixer 205 and IF filter 207 provides some filtering of the signal being processed through each channel. The gain of IF filter 207 is set by set-point 208.
The phase reference for phase detectors 210 is determined from the channel containing left sensor 201 by phase-lock-loop 209. The output signals from the two channels are summed, after being independently processed, in adder 211. The output signal from adder 211 is the left/right signal. The polarity of the left/right signal indicates whether center sensor 203 is laterally displaced to the left or right of line 4.
This method of line detection, however, is subject to phase instability. Because of the difficulty inherent in insuring that the output signals from left sensor 201 and right sensor 202 remain comparable over the full range of input signal strength, as is required by this method of signal processing, little signal filtering can be accomplished in the two channels. Additionally, because the phase reference is determined using the output signal from left sensor 201, line locator 200 is incapable of left/right location if left sensor 201 and right sensor 202 are both displaced to one side of line 4 where the output signals from both sensors have the same polarity.
Other line locators, such as U.S. Pat. No. 5,001,430 to Peterman et al., having a left/right detection capability include a left sensor, a right sensor and a central sensor where the left sensor and the right sensor have an orientation of between 0xc2x0 and 90xc2x0 from the horizontal, but specifically not 0xc2x0 or 90xc2x0. In addition, because the left sensor and the right sensor detect magnetic fields having the same polarities (i.e., primarily the horizontal component of the magnetic field), the output signal used in the circuitry is a difference signal between the magnetic field measured at the left sensor and the magnetic field measured at the right sensor. As a result, the output signal of the left/right detector is typically small and difficult to process.
There remains a need for a line locator having reliable lateral position indication (i.e., indication of which side of the line that the locator is positioned). In addition, there is a need for a line locator having horizontal position indication along with the capability of indicating the depth of the line. Finally, there is a need for a line locator having the capability of displaying a calibrated distance corresponding to an amount that the line locator is translated from the line (as opposed to simply indicating which side of the line the locator is positioned).
Accordingly, a line locator having the capability of indicating whether the line locator is to the left of a line or to the right of the line is described. The output signal from a left sensor is convoluted with the output signal from a right sensor before filtering so that phase and amplitude information is not lost and further filtering of the convoluted output signal can be accomplished. The convoluted signal is processed through a single channel that relieves the necessity for accurate tracking of signals through separate channels.
In addition, phase detection is accomplished using a phase reference signal acquired from sources other than the left sensor or the right sensor. In some embodiments, the phase reference signal can be acquired from a transmitter that is being used to excite the line. The transmitter can be electrically coupled to the line locator by any convenient method, including direct electrical connection or wireless communication. In addition, the line may be utilized as a transmitter antenna for wireless communication of a phase reference signal. In other embodiments, the phase reference signal is generated using a magnetic field sensor not associated with the left/right locator sensors. For example, another horizontally oriented sensor, where the output signal from the sensor does not change polarity when passed over the line, can be used to generate the phase reference signal.
Although the left sensor and the right sensor can have any orientation, orientations of the left sensor and the right sensor that lie directly along the magnetic field orientation will provide the maximum output signals. Signal processing circuitry compares the output signal of the left sensor and the output signal of the right sensor in order to determine the lateral position of the line locator relative to the line. The comparison of the output signals include convoluting the output signal from the left sensor with the output signal from the right sensor.
Convolutions of the two output signals include taking their sum or their difference. Output signals from the left and right sensors may also be convoluted in other fashions in order to analyze the lateral position. The actual convolution is dependent on the orientation of the sensors. If the sensors are vertically oriented, for example, then a convenient and useful convolution function is an addition.
Some embodiments of the line locator include a field sensor. The processing circuit that includes the field sensor provides a phase reference to the signal processing circuitry and may provide other signals such as an AGC signal. Some embodiments of the invention include two center sensors, one located directly above the other, so that the line locator can determine the depth of the line and, from the depth, determine actual calibrated lateral position of the line locator position relative to the line.
Several embodiments of the invention are discussed below with reference to the following figures.